1. Field of the Invention
This invention relates to a method of calibrating a sensor for determining the partial pressure of a gas, more particularly a cutaneous sensor for the cutaneous determination of blood oxygen and carbon dioxide levels, and to the apparatus for the implementation of the method. The term "calibration" as used herein is to be understood in the broad sense of covering both calibration and functional testing, i.e., testing the measurement characteristic of the sensor.
2. Description of the Art
It is fairly simple to calibrate oxygen sensors operating on the principle of the Clark electrode, since calibration can be performed using atmospheric air with the sensor electrode connected to the measuring device. Since during calibration the measuring device cannot be used for patient monitoring, a disadvantage of this method is that valuable operating time is lost. There is always a risk that the measuring device will need to be calibrated at the precise moment when it is urgently required. The only way of obviating this problem is for a hospital ward to have a correspondingly large number of devices available.
The problem is even more difficult in the case of carbon dioxide sensors. They cannot be calibrated using atmospheric air but must be calibrated by a special device which produces mixed gases suitable for calibration.
Theoretically it is unnecessary to provide a calibration device for each measuring device since a single calibration device can be used to calibrate a number of measuring devices. However, the problems just described in relation to oxygen sensors are further aggravated by the overlapping of the operating times of the measuring devices and the calibration device, so that in practice more calibration devices are needed than would be strictly necessary to calibrate a particular number of measuring devices. Also, to carry out a calibration the calibration device must always be brought to the measuring device or vice versa, thus imposing extra work on the personnel of a hospital.
The present invention provides a method of calibrating partial pressure sensors which obviates these disadvantages so that the measuring devices can be available for use permanently and at any required time.